Coal

Coal is a fossil fuel, commonly used to produce electricity, that is formed from the decomposition of organic materials that have been subjected to geologic heat and pressure over millions of years. Coal is considered a nonrenewable resource because it cannot be replenished on a human time frame.

The "lifecycle" of coal is a long one, with many environmentally harmful steps. The activities involved in generating electricity from coal include mining, transport to power plants and burning of the coal in power plants. When burned, numerous greenhouse gases are released, making it one of the biggest contributors to global warming.

Coal reserves in the U.S. stand at 268 billion tons, of which 43 percent are in surface mines. The three major coal-producing states are Wyoming, West Virginia and Kentucky. (Source: EPA / Photo: ZUMA Press)